Earth’s Early History

1. Earth’s Early History Section 17-2

2. Formation of the Universe • The theory of the “big bang” states that the universe was concentrated into one super dense mass that expanded (13.7 BYA)

3. Formation of Earth • Evidence shows that Earth was not “born” in a single event • Pieces of cosmic debris were probably attracted to one another over the course of 100 million years • A collision of an object with young Earth (4.6 BYA) produced heat that melted the entire globe

4. Once Earth melted, its elements arranged themselves according to density • most dense core • moderately dense  crust • least dense  atmosphere • The first atmosphere probably contained cyanide, NH3 ,CH4, CO2, CO, N2, hydrogen sulfide, and H20 vapor • note the 4 elements present: C, O, H, N

5. Why this early Earth couldn’t support life • organic molecules don’t form easily in the presence of N and CO2 • no ozone (O3) layer so UV radiation from the sun would harm DNA • no free O2 • frequent volcanic eruptions and violent lightning storms • extreme temperature variations (no greenhouse effect)

6. More Changes • About 4 billion years ago, Earth cooled enough to form solid rocks on its surface • Around 3.8 billion years ago, the surface cooled enough for water to remain a liquid • soon oceans covered much of the surface

7. The First Organic Molecules • Given these conditions, scientists believe that organic molecules could have evolved. • evidence from meteorites shows that organic compounds form in space • organic compounds continue to form at volcanic vents deep in the ocean

8. Creating Life in the Lab • In the 1950s, Miller and Urey recreated the conditions of early Earth in a lab • included volcanic gases, energy from heat & electricity and water vapor • formed simple amino acids in only a few days!

9. Spark simulating lightning storms Mixture of gases simulating atmosphere of early Earth Miller and Urey’s Experiment Condensation chamber Water vapor Cold water cools chamber, causing droplets to form. Liquid containing amino acids and other organic compounds

10. The Puzzle of Life’s Origin • When organic molecules accumulated in the oceans it was like a soup. • Scientists named Oparin & Haldane came up with this hypothesis in the 1920s and called it Primordial Soup • Life evolved from further chemical reactions and transformations • first life forms were heterotrophs that fed on the organic compounds in primordial soup

11. Free Oxygen • microscopic fossils, or microfossils, of prokaryotic organisms resembling modern bacteria have been found in rocks over 3.5 billion years old • these first life-forms would have evolved without oxygen

12. about 2.2 BYA, photosynthetic bacteria began to pump oxygen into the oceans • next, oxygen gas accumulated in the atmosphere, but wasn’t abundant until 600-800 MILLION years ago • The rise in O2 in the atmosphere drove some life forms to extinction, while others developed new, more efficient metabolic pathways that used O2 for respiration

13. The Endosymbiotic Theory • The endosymbiotic theory proposes that eukaryotic cells arose from living communities of prokaryotic organisms. • the hypothesis was proposed over a century ago, but did not receive support from the scientific community until Lynn Margulis of BU unveiled key evidence in the 1960s

14. Ancient Prokaryotes Chloroplast Plants and plantlike protists Aerobic bacteria Photosynthetic bacteria Nuclear envelope evolving Mitochondrion Primitive Photosynthetic Eukaryote Animals, fungi, and non-plantlike protists Primitive Aerobic Eukaryote Ancient Anaerobic Prokaryote

15. 15-1 The Puzzle of Life’s Diversity Voyage of the Beagle • In 1831, a naturalist by the name of Charles Darwin set sail from England aboard the H.M.S. Beagle for a voyage around the world

16. He went ashore and collected plant and animal specimens for his collection • He studied the specimens, read the latest scientific books, and filled many notebooks with his observations and thoughts.

17. During his travels, Darwin made numerous observations and collected evidence that led him to propose a hypothesis about the way life changes over time. •  the theory of evolution

18. Darwin’s Observations • He observed that many plants and animals were well suited to the environment they inhabited. • He was impressed by the ways in which organisms survived and produced offspring

19. Living Organisms and Fossils • Some things that Darwin collected were the preserved remains of ancient organisms, called fossils. • some resembled organisms that were still alive • others looked completely unlike any creature he had ever seen

20. The Galápagos Islands • Darwin observed that the Galápagos Islands were close together, but had very different climates • He also noticed that the characteristics of many animals and plants varied noticeably among the different islands

22. Darwin wondered if animals living on different islands had once been members of the same species. • could have evolved from an original South American ancestor species

23. 15-2 Ideas that Shaped Darwin’s Thinking An Ancient, Changing Earth • In 1785 James Hutton helped scientists recognize that Earth is many millions of years old

24. In 1833 Charles Lyell published works that said the processes that changed Earth in the past are the same processes that operate in the present

25. So Darwin thought: • If the Earth could change over time, life might change as well. • It would have taken many years for life to change in the way Lyell suggested  Earth would have to be extremely old

26. Lamarck’s Evolution Hypothesis • In 1809 Jean-Baptiste Lamarck published his ideas on how species inherit acquired traits • He recognized that: • living things have changed over time • all species were descended from other species • organisms were adapted to their environment

27. He proposed that: • by selective use or disuse of organs, organisms acquired or lost traits during their lifetime • these traits could be passed to offspring • over time, this led to a change in the species

28. WRONG!

30. Evaluating Lamarck’s Hypothesis • Lamarck’s hypotheses about evolution were incorrect in several ways • He didn’t know: • how traits are inherited • that an organisms behavior has no effect on its heritable characteristics • However, he paved the way for the work of later biologists!

31. Population Growth • In 1798, Thomas Malthus reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone • When Darwin read Malthus’ work, he applied this reasoning to plants and animals • a single species could overrun the world • this idea was central to Darwin’s explanation of evolutionary change

32. 15-3 Darwin Presents His Case Publication of On the Origin of Species • Darwin filled notebooks with his ideas about species diversity and the evolution process • He was stunned and disturbed by his discoveries • He shelved his manuscript for many years and told his wife to publish it in case he died

33. In 1858, Darwin received a short essay from naturalist Alfred Wallace • it summarized Darwin’s thoughts on evolutionary change • pushed Darwin to publish his book, On the Origin of Species, in 1859 • book proposed a mechanism for evolution called natural selection • presented evidence that evolution has been taking place for millions of years and continues in all living things

34. Inherited Variation & Artificial Selection • Darwin noticed that plant and animal breeders would breed only the largest hogs, fastest horses, or the cows that produced the most milk • he called this artificial selection • uses useful traits from the natural variation among different organisms

36. Evolution and Natural Selection • Darwin compared processes in nature to artificial selection and developed a scientific hypothesis to explain how evolution occurs • he notice that high birth rates and a shortage of life’s basic needs would force organisms to compete for resources • the struggle for existence was central to Darwin’s theory of evolution

37. Survival of the Fittest • fitness = the ability of an individual to survive and reproduce in its specific environment • Darwin proposed that fitness is the result of adaptations • an adaptation is any inherited characteristic that increases an organism’s chance of survival

38. Individuals with characteristics that are not well suited to their environment either die or leave few offspring. • Those better suited to their environment survive and reproduce most successfully. • Darwin called this survival of the fittest

39. Because of its similarities to artificial selection, Darwin referred to survival of the fittest as natural selection. • Over time, natural selection results in changes in the inherited characteristics of a population. These changes increase a species’ fitness in its environment.

41. Descent with Modification • Each living species has descended, with changes, from other species over time. • Darwin referred to this principle as descent with modification • implies that all living organisms are related to one another (common descent)

42. Evidence of Evolution • The fossil record • Darwin saw this as a record of the history of life on Earth • by comparing fossils from different rock layers scientists could document that life had changed over time

43. The geographical distribution of living species • Darwin thought that the Galápagos finches could have descended with modification from a common mainland ancestor

44. Homologous body structures • these are structures that have different mature forms, but develop from the same embryonic tissue • similarities and differences help biologists group animals according to how recently they shared a common ancestor

45. Not all homologous structures serve important functions. • The organs of many animals are so reduced in size that they are just vestiges, or traces, of homologous organs in other species. • These organs are called vestigial organs.

46. Similarities in embryology • the embryos of many vertebrates are very similar • the same groups of embryonic cells develop in the same order and in similar patterns to produce the tissues and organs of all vertebrates

48. 17.4 Patterns of Evolution • Macroevolutionrefers to large-scale evolutionary patterns and processes that occur over long periods of time • Six important topics are: • extinction • adaptive radiation • convergent evolution • coevolution • punctuated equilibrium • changes in developmental genes

49. Extinction • More than 99% of all species that have ever lived are now extinct. • Mass extinctions have: • provided ecological opportunities for organisms that survived • resulted in bursts of evolution that produced many new species

50. Adaptive Radiation • Adaptive radiationis the process by which a single species or a small group of species evolves into several different forms that live in different ways. • Ex: Darwin's finches - more than a dozen species evolved from a single species. • can occur on a much larger scale • disappearance of dinosaurs  adaptive radiation of mammals